1. Field of the Invention
The present invention relates to a voltage generating apparatus.
2. Description of Related Art
With blooming development of electronic technology, electronic products with various functions are provided. Since the electronic products are widely used, and marketing of the electronic products is global, a same kind of electronic product has to work normally under totally different environments. For example, a same kind of mobile phone will be sold to high-latitude countries with cold weather, and may also be sold to countries around the equator with hot weather. Or, a same mobile phone needs to be used under different environments due to relocation of a user. To cope with the aforementioned requirements, design of a circuit with a relatively high adaptability for different environments has become one of the major subjects to various designers.
In all electronic systems, there always exists some irreplaceable analog circuits, and these analog circuits generally require an accurate reference power supply for stability of circuit performance. Therefore, a plurality of so-called bandgap voltage generating apparatus is provided. A main feature of the bandgap voltage generating apparatus is its self-compensation capability of output voltage thereof when temperature is changed. FIG. 1 is a diagram of a conventional voltage generating apparatus having a temperature compensation capability. In the conventional voltage generating apparatus, features that collector current of two bipolar junction transistors (BJTs) Q1 and Q2 will be increased along with temperature (i.e. the so-called positive temperature coefficient) will be used for compensating an emitter-base voltage of the BJT which is decreased with increase of the temperature (i.e. the so-called negative temperature coefficient), so as to maintain an output voltage VREF unchanged.
However, besides requirement of outputting an accurate and stable voltage, control of power consumption of the circuit is also important. In the conventional voltage generating apparatus as shown in FIG. 1, since an input voltage of an amplifier AMP is limited, the amplifier AMP requires a relatively high system voltage for working normally, such that power consumption of the whole voltage generating apparatus is relatively high. Therefore, another voltage generating apparatus is provided, as shown in FIG. 2. FIG. 2 is a diagram illustrating a conventional voltage generating apparatus, in which the input voltage of the amplifier AMP is first divided by a resistor-series, and then is input to the amplifier AMP, and in coordination with a new amplifier AMP input circuit, working voltage of the amplifier AMP will be reduced, and accordingly power consumption thereof is reduced. By applying a new output circuit, the conventional voltage generating apparatus may generate an output voltage VREF of less than 1 volt.
FIG. 3 and FIG. 4 are diagrams respectively illustrating another conventional voltage generating apparatus. Different from the aforementioned conventional voltage generating apparatus, the voltage generating apparatus of FIG. 3 and FIG. 4 is composed of complementary metal oxide semiconductor. field effect transistors (CMOFETSs). Features of such kind of voltage generating apparatus is that cost of the CMOSFETs is relatively low, and the voltage generating apparatus applying the CMOSFETs is much easier to the output voltage VREF of less than 1 volt compared to the aforementioned voltage generating apparatus applying the BJTs.
FIG. 5 is a diagram illustrating a conventional voltage generating apparatus without any resistors. Such conventional voltage generating apparatus applies two current sources to turn on a diode D1 and a diode D2, so as to provide a voltage V1 and a voltage V2 to function as input voltages for two differential pairs 501 and 502. Wherein, the voltage V1 and the voltage V2 respectively have a negative temperature coefficient. Based on a ratio between the differential pair 501 and the differential pair 502, the output voltage VREF is composed of the voltage V2 and a difference between the voltage V2 and the voltage V1. Since the difference between the voltage V2 and the voltage V1 has the positive temperature coefficient, it may compensate the negative temperature coefficient of the voltage V2, such that the output voltage VREF remains unchanged when the temperature is changed.
FIG. 6 is a diagram illustrating an embodiment of a conventional voltage generating apparatus of FIG. 5 without resistors. Operational principle of this conventional voltage generating apparatus is the same to the circuit shown in FIG. 5, and therefore the description thereof is not repeated.